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<tr class="t-nv-h2"><td colspan="5">概述</td></tr>
<tr class="t-nv"><td colspan="5"> <a href="classes.html" title="cpp/language/classes">综述</a> </td></tr>
<tr class="t-nv"><td colspan="5"> <strong class="selflink"><code>class</code>/<code>struct</code> 类型</strong> </td></tr>
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<tr class="t-nv"><td colspan="5"> <a href="using_declaration.html" title="cpp/language/using declaration"><code>using</code> 声明</a></td></tr>
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<p>类（class）与结构体（struct）是用户定义类型，以 <span class="t-spar">类说明符</span> 定义，它在<a href="declarations.html" title="cpp/language/declarations">声明</a>语法的 <span class="t-spar">声明说明符序列</span> 中出现。类说明符拥有下列语法：
</p>
<table class="t-sdsc-begin">

<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr>
<tr class="t-sdsc">
<td class="t-sdsc-nopad"> <span class="t-spar">类关键词</span> <span class="t-spar">attr</span> <span class="t-spar">类头名</span> <span class="t-spar">基类子句</span> <code><b>{ </b></code> <span class="t-spar">成员说明</span> <code><b>} </b></code>
</td>
<td class="t-sdsc-nopad">
</td>
<td class="t-sdsc-nopad">
</td></tr>



<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr></table>
<table class="t-par-begin">


<tr class="t-par">
<td>  <span class="t-spar">类关键词</span>
</td>
<td> -
</td>
<td>  <a href="../keyword/class.html" title="cpp/keyword/class">class</a> 或 <a href="../keyword/struct.html" title="cpp/keyword/struct">struct</a> 之一。除了默认<a href="access.html" title="cpp/language/access">成员访问</a>和默认<a href="derived_class.html" title="cpp/language/derived class">基类访问</a>之外，两个关键词是等同的。
</td></tr>
<tr class="t-par">
<td>  <span class="t-spar">attr</span><span class="t-mark-rev t-since-cxx11">(C++11)</span>
</td>
<td> -
</td>
<td>  可选的任何数量<a href="attributes.html" title="cpp/language/attributes">属性</a>序列，可包含 <a href="alignas.html" title="cpp/language/alignas">alignas 指定符</a>
</td></tr>
<tr class="t-par">
<td>  <span class="t-spar">类头名</span>
</td>
<td> -
</td>
<td>  所定义的类的名字。可选地<a href="name.html#.E6.9C.89.E9.99.90.E5.AE.9A.E7.9A.84.E6.A0.87.E8.AF.86.E7.AC.A6" title="cpp/language/identifiers">有限定</a>，可选地后随关键词 <a href="../keyword/final.html" title="cpp/keyword/final">final</a>。名字可以省略，该情况下类是无名的（注意无名类不能为 <a href="final.html" title="cpp/language/final">final</a>）
</td></tr>
<tr class="t-par">
<td>  <span class="t-spar">基类子句</span>
</td>
<td> -
</td>
<td>  一或多个父类以及各自所用的继承模型的可选列表（见<a href="derived_class.html" title="cpp/language/derived class">派生类</a>）
</td></tr>
<tr class="t-par">
<td>  <span class="t-spar">成员说明</span>
</td>
<td> -
</td>
<td>  访问说明符、成员对象及成员函数的声明和定义的列表（见下文）
</td></tr></table>
<p>语法综述见<a href="classes.html" title="cpp/language/classes">类</a>。若 <span class="t-spar">类关键词</span> 为 <code>union</code>，则声明引入一个<a href="union.html" title="cpp/language/union">联合体类型</a>。 
</p>
<h3><span class="mw-headline" id=".E5.89.8D.E7.BD.AE.E5.A3.B0.E6.98.8E">前置声明</span></h3>
<p>下列形式的声明
</p>
<table class="t-sdsc-begin">

<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr>
<tr class="t-sdsc">
<td class="t-sdsc-nopad"> <span class="t-spar">类关键词</span> <span class="t-spar">attr</span> <span class="t-spar">标识符</span> <code><b>;</b></code>
</td>
<td class="t-sdsc-nopad">
</td>
<td class="t-sdsc-nopad">
</td></tr>



<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr></table>
<p>声明一个将稍后在此作用域定义的类类型。直到定义出现前，此类名具有<a href="incomplete_type.html#.E4.B8.8D.E5.AE.8C.E6.95.B4.E7.B1.BB.E5.9E.8B" title="cpp/language/type">不完整类型</a>。这允许类之间彼此引用：
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="cpp source-cpp"><pre class="de1"><span class="kw1">class</span> Vector<span class="sy4">;</span> <span class="co1">// 前置声明</span>
<span class="kw1">class</span> Matrix <span class="br0">{</span>
    <span class="co1">// ...</span>
    <span class="kw1">friend</span> Vector operator<span class="sy2">*</span><span class="br0">(</span><span class="kw4">const</span> Matrix<span class="sy3">&amp;</span>, <span class="kw4">const</span> Vector<span class="sy3">&amp;</span><span class="br0">)</span><span class="sy4">;</span>
<span class="br0">}</span><span class="sy4">;</span>
<span class="kw1">class</span> Vector <span class="br0">{</span>
    <span class="co1">// ...</span>
    <span class="kw1">friend</span> Vector operator<span class="sy2">*</span><span class="br0">(</span><span class="kw4">const</span> Matrix<span class="sy3">&amp;</span>, <span class="kw4">const</span> Vector<span class="sy3">&amp;</span><span class="br0">)</span><span class="sy4">;</span>
<span class="br0">}</span><span class="sy4">;</span></pre></div></div>
<p>而且若特定的源文件仅使用到该类的指针和引用，这亦使得减少 #include 依赖成为可能：
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="cpp source-cpp"><pre class="de1"><span class="co1">// 在 MyStruct.h 中</span>
<span class="co2">#include &lt;iosfwd&gt; // 含有 std::ostream 的前置声明</span>
<span class="kw1">struct</span> MyStruct <span class="br0">{</span>
    <span class="kw4">int</span> value<span class="sy4">;</span>
    <span class="kw1">friend</span> <a href="../io/basic_ostream.html"><span class="kw1729">std::<span class="me2">ostream</span></span></a><span class="sy3">&amp;</span> operator<span class="sy1">&lt;&lt;</span><span class="br0">(</span><a href="../io/basic_ostream.html"><span class="kw1729">std::<span class="me2">ostream</span></span></a><span class="sy3">&amp;</span> os, <span class="kw4">const</span> S<span class="sy3">&amp;</span> s<span class="br0">)</span><span class="sy4">;</span>
    <span class="co1">// 其定义在 MyStruct.cpp 文件中提供，该文件使用 #include &lt;ostream&gt;</span>
<span class="br0">}</span><span class="sy4">;</span></pre></div></div>
<p>若前置声明出现于局部作用域，则它<i>隐藏</i>其外围作用域中可出现的先前声明的相同名字的类、变量、函数，以及所有其他声明：
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="cpp source-cpp"><pre class="de1"><span class="kw1">struct</span> s <span class="br0">{</span> <span class="kw4">int</span> a<span class="sy4">;</span> <span class="br0">}</span><span class="sy4">;</span>
<span class="kw1">struct</span> s<span class="sy4">;</span> <span class="co1">// 不做任何事（s 已定义于此作用域）</span>
<span class="kw4">void</span> g<span class="br0">(</span><span class="br0">)</span> <span class="br0">{</span>
    <span class="kw1">struct</span> s<span class="sy4">;</span> <span class="co1">// 新的局部类“s”的前置声明</span>
              <span class="co1">// 它隐藏全局的 struct s 直至此块结尾</span>
    s<span class="sy2">*</span> p<span class="sy4">;</span>     <span class="co1">// 指向局部 struct s 的指针</span>
    <span class="kw1">struct</span> s <span class="br0">{</span> <span class="kw4">char</span><span class="sy2">*</span> p<span class="sy4">;</span> <span class="br0">}</span><span class="sy4">;</span> <span class="co1">// 局部 struct s 的定义</span>
<span class="br0">}</span></pre></div></div>
<p>注意，通过作为其他声明一部分的<a href="elaborated_type_specifier.html" title="cpp/language/elaborated type specifier">详述类型说明符</a>，也可以引入新的类名，但仅当<a href="lookup.html" title="cpp/language/lookup">名字查找</a>无法找到先前声明的有此名的类时才行。
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="cpp source-cpp"><pre class="de1"><span class="kw1">class</span> U<span class="sy4">;</span>
<span class="kw1">namespace</span> ns<span class="br0">{</span>
    <span class="kw1">class</span> Y f<span class="br0">(</span><span class="kw1">class</span> T p<span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 声明函数 ns::f 并声明 ns::T 与 ns::Y</span>
    <span class="kw1">class</span> U f<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// U 指代 ::U</span>
    Y<span class="sy2">*</span> p<span class="sy4">;</span> T<span class="sy2">*</span> q<span class="sy4">;</span> <span class="co1">// 可使用到 T 和 Y 的指针及引用</span>
<span class="br0">}</span></pre></div></div>
<h3><span class="mw-headline" id=".E6.88.90.E5.91.98.E8.AF.B4.E6.98.8E">成员说明</span></h3>
<p>成员说明，或类定义的<i>体</i>，是花括号环绕的任何数量下列各项的序列：
</p>
<div class="t-li1"><span class="t-li">1)</span> 具有下列形式的成员声明
<table class="t-sdsc-begin">

<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr>
<tr class="t-sdsc">
<td class="t-sdsc-nopad"> <span class="t-spar">attr</span><span class="t-mark">(可选)</span> <span class="t-spar">声明说明符序列</span><span class="t-mark">(可选)</span> <span class="t-spar">成员声明符列表</span><span class="t-mark">(可选)</span> <code><b>;</b></code>
</td>
<td class="t-sdsc-nopad">
</td>
<td class="t-sdsc-nopad">
</td></tr>



<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr></table>
<table class="t-par-begin">


<tr class="t-par">
<td>  <span class="t-spar">attr</span><span class="t-mark-rev t-since-cxx11">(C++11)</span>
</td>
<td> -
</td>
<td>  可选的任何数量<a href="attributes.html" title="cpp/language/attributes">属性</a>序列
</td></tr>
<tr class="t-par">
<td>  <span class="t-spar">声明说明符序列</span>
</td>
<td> -
</td>
<td>  <a href="declarations.html#.E8.AF.B4.E6.98.8E.E7.AC.A6" title="cpp/language/declarations">说明符</a>的序列。它只在构造函数，析构函数，以及用户定义<a href="cast_operator.html" title="cpp/language/cast operator">转换函数</a>中可选。
</td></tr>
<tr class="t-par">
<td>  <span class="t-spar">成员声明符列表</span>
</td>
<td> -
</td>
<td>  与 <a href="declarations.html" title="cpp/language/declarations">初始化声明符列表</a>相同，但额外允许<a href="bit_field.html" title="cpp/language/bit field">位域定义</a>、<a href="abstract_class.html" title="cpp/language/abstract class">纯说明符</a><span class="t-rev-inl t-since-cxx11"><span>和虚说明符（ <code><a href="override.html" title="cpp/language/override">override</a></code> 或 <code><a href="final.html" title="cpp/language/final">final</a></code>）</span> <span><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></span></span>，并且不允许<a href="direct_initialization.html" title="cpp/language/direct initialization">直接非列表初始化语法</a>。
</td></tr></table>
<p>这种声明可以声明<a href="static.html" title="cpp/language/static">静态</a>及非静态的<a href="data_members.html" title="cpp/language/data members">数据成员</a>与<a href="member_functions.html" title="cpp/language/member functions">成员函数</a>、成员 <a href="typedef.html" title="cpp/language/typedef">typedef</a>、成员<a href="enum.html" title="cpp/language/enum">枚举</a>以及<a href="nested_classes.html" title="cpp/language/nested types">嵌套类</a>。它亦可为<a href="friend.html" title="cpp/language/friend">友元声明</a>。
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="cpp source-cpp"><pre class="de1"><span class="kw1">class</span> S <span class="br0">{</span>
    <span class="kw4">int</span> d1<span class="sy4">;</span> <span class="co1">// 非静态数据成员</span>
    <span class="kw4">int</span> a<span class="br0">[</span><span class="nu0">10</span><span class="br0">]</span> <span class="sy1">=</span> <span class="br0">{</span><span class="nu0">1</span>,<span class="nu0">2</span><span class="br0">}</span><span class="sy4">;</span> <span class="co1">// 带初始化器的非静态数据成员 (C++11)</span>
    <span class="kw4">static</span> <span class="kw4">const</span> <span class="kw4">int</span> d2 <span class="sy1">=</span> <span class="nu0">1</span><span class="sy4">;</span> <span class="co1">// 带初始化器的静态数据成员</span>
    <span class="kw1">virtual</span> <span class="kw4">void</span> f1<span class="br0">(</span><span class="kw4">int</span><span class="br0">)</span> <span class="sy1">=</span> <span class="nu0">0</span><span class="sy4">;</span> <span class="co1">// 纯虚成员函数</span>
    <a href="../string/basic_string.html"><span class="kw1230">std::<span class="me2">string</span></span></a> d3, <span class="sy2">*</span>d4, f2<span class="br0">(</span><span class="kw4">int</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 两个数据成员和一个成员函数</span>
    <span class="kw2">enum</span> <span class="br0">{</span>NORTH, SOUTH, EAST, WEST<span class="br0">}</span><span class="sy4">;</span>
    <span class="kw1">struct</span> NestedS <span class="br0">{</span>
        <a href="../string/basic_string.html"><span class="kw1230">std::<span class="me2">string</span></span></a> s<span class="sy4">;</span>
    <span class="br0">}</span> d5, <span class="sy2">*</span>d6<span class="sy4">;</span>
    <span class="kw1">typedef</span> NestedS value_type, <span class="sy2">*</span>pointer_type<span class="sy4">;</span>
<span class="br0">}</span><span class="sy4">;</span></pre></div></div></div>
<div class="t-li1"><span class="t-li">2)</span> 函数定义，同时声明并定义<a href="member_functions.html" title="cpp/language/member functions">成员函数</a>或者<a href="friend.html" title="cpp/language/friend">友元函数</a>。成员函数定义之后的分号是可选的。所有定义于类体之内的函数自动为<a href="inline.html" title="cpp/language/inline">内联</a>的
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="cpp source-cpp"><pre class="de1"><span class="kw1">class</span> M <span class="br0">{</span>
    <a href="../types/size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> C<span class="sy4">;</span>
    <a href="../container/vector.html"><span class="kw1269">std::<span class="me2">vector</span></span></a><span class="sy1">&lt;</span><span class="kw4">int</span><span class="sy1">&gt;</span> data<span class="sy4">;</span>
 <span class="kw1">public</span><span class="sy4">:</span>
    M<span class="br0">(</span><a href="../types/size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> R, <a href="../types/size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> C<span class="br0">)</span> <span class="sy4">:</span> C<span class="br0">(</span>C<span class="br0">)</span>, data<span class="br0">(</span>R<span class="sy2">*</span>C<span class="br0">)</span> <span class="br0">{</span><span class="br0">}</span> <span class="co1">// 构造函数定义</span>
    <span class="kw4">int</span> operator<span class="br0">(</span><span class="br0">)</span><span class="br0">(</span>size_t r, size_t c<span class="br0">)</span> <span class="kw4">const</span> <span class="br0">{</span> <span class="co1">// 成员函数定义</span>
        <span class="kw1">return</span> data<span class="br0">[</span>r<span class="sy2">*</span>C<span class="sy2">+</span>c<span class="br0">]</span><span class="sy4">;</span>
    <span class="br0">}</span>
    <span class="kw4">int</span><span class="sy3">&amp;</span> operator<span class="br0">(</span><span class="br0">)</span><span class="br0">(</span>size_t r, size_t c<span class="br0">)</span> <span class="br0">{</span>  <span class="co1">// 另一个成员函数定义</span>
        <span class="kw1">return</span> data<span class="br0">[</span>r<span class="sy2">*</span>C<span class="sy2">+</span>c<span class="br0">]</span><span class="sy4">;</span>
    <span class="br0">}</span>
<span class="br0">}</span><span class="sy4">;</span></pre></div></div></div>
<div class="t-li1"><span class="t-li">3)</span> <a href="access.html" title="cpp/language/access">访问说明符</a> <code>public:</code>、<code>protected:</code> 和 <code>private:</code>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="cpp source-cpp"><pre class="de1"><span class="kw1">class</span> S <span class="br0">{</span>
 <span class="kw1">public</span><span class="sy4">:</span>
    S<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>          <span class="co1">// 公开构造函数</span>
    S<span class="br0">(</span><span class="kw4">const</span> S<span class="sy3">&amp;</span><span class="br0">)</span><span class="sy4">;</span>  <span class="co1">// 公开复制构造函数</span>
    <span class="kw1">virtual</span> ~S<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 公开虚析构函数</span>
 <span class="kw1">private</span><span class="sy4">:</span>
    <span class="kw4">int</span><span class="sy2">*</span> ptr<span class="sy4">;</span> <span class="co1">// 私有数据成员</span>
<span class="br0">}</span><span class="sy4">;</span></pre></div></div></div>
<div class="t-li1"><span class="t-li">4)</span> <a href="using_declaration.html" title="cpp/language/using declaration">using 声明</a>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="cpp source-cpp"><pre class="de1"><span class="kw1">class</span> Base <span class="br0">{</span>
 <span class="kw1">protected</span><span class="sy4">:</span>
     <span class="kw4">int</span> d<span class="sy4">;</span>
<span class="br0">}</span><span class="sy4">;</span>
<span class="kw1">class</span> Derived <span class="sy4">:</span> <span class="kw1">public</span> Base <span class="br0">{</span>
 <span class="kw1">public</span><span class="sy4">:</span>
    <span class="kw1">using</span> Base<span class="sy4">::</span><span class="me2">d</span><span class="sy4">;</span> <span class="co1">// 令 Base 的受保护成员 d 为 Derived 的公开成员</span>
    <span class="kw1">using</span> Base<span class="sy4">::</span><span class="me2">Base</span><span class="sy4">;</span> <span class="co1">// 继承父类的全部构造函数 (C++11)</span>
<span class="br0">}</span><span class="sy4">;</span></pre></div></div></div>
<div class="t-li1"><span class="t-li">5)</span> <a href="static_assert.html" title="cpp/language/static assert">static_assert</a> 声明
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="cpp source-cpp"><pre class="de1"><span class="kw1">template</span><span class="sy1">&lt;</span><span class="kw1">typename</span> T<span class="sy1">&gt;</span>
<span class="kw1">struct</span> Foo <span class="br0">{</span>
  static_assert<span class="br0">(</span><a href="../types/is_floating_point.html"><span class="kw458">std::<span class="me2">is_floating_point</span></span></a><span class="sy1">&lt;</span>T<span class="sy1">&gt;</span><span class="sy4">::</span><span class="me2">value</span>, <span class="st0">"Foo&lt;T&gt;: T must be floating point"</span><span class="br0">)</span><span class="sy4">;</span>
<span class="br0">}</span><span class="sy4">;</span></pre></div></div></div>
<div class="t-li1"><span class="t-li">6)</span> <a href="member_template.html" title="cpp/language/member template">成员模板声明</a>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="cpp source-cpp"><pre class="de1"><span class="kw1">struct</span> S <span class="br0">{</span>
    <span class="kw1">template</span><span class="sy1">&lt;</span><span class="kw1">typename</span> T<span class="sy1">&gt;</span>
    <span class="kw4">void</span> f<span class="br0">(</span>T<span class="sy3">&amp;&amp;</span> n<span class="br0">)</span><span class="sy4">;</span>
 
    <span class="kw1">template</span><span class="sy1">&lt;</span><span class="kw1">class</span> CharT<span class="sy1">&gt;</span>
    <span class="kw1">struct</span> NestedS <span class="br0">{</span>
        <a href="../string/basic_string.html"><span class="kw1228">std::<span class="me2">basic_string</span></span></a><span class="sy1">&lt;</span>CharT<span class="sy1">&gt;</span> s<span class="sy4">;</span>
    <span class="br0">}</span><span class="sy4">;</span>
<span class="br0">}</span><span class="sy4">;</span></pre></div></div></div>
<div class="t-li1"><span class="t-li">7)</span> <a href="type_alias.html" title="cpp/language/type alias">别名声明</a>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="cpp source-cpp"><pre class="de1"><span class="kw1">template</span> <span class="sy1">&lt;</span><span class="kw1">typename</span> T<span class="sy1">&gt;</span>
<span class="kw1">struct</span> identity
<span class="br0">{</span>
    <span class="kw1">using</span> type <span class="sy1">=</span> T<span class="sy4">;</span>
<span class="br0">}</span><span class="sy4">;</span></pre></div></div></div>
 <table class="t-rev-begin">
<tr class="t-rev t-since-cxx17"><td>
<div class="t-li1"><span class="t-li">8)</span> 成员类模板的<a href="class_template_argument_deduction.html" title="cpp/language/class template argument deduction">推导指引</a>：
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="cpp source-cpp"><pre class="de1"><span class="kw1">struct</span> S <span class="br0">{</span>
    <span class="kw1">template</span><span class="sy1">&lt;</span><span class="kw1">class</span> CharT<span class="sy1">&gt;</span>
    <span class="kw1">struct</span> NestedS <span class="br0">{</span>
        <a href="../string/basic_string.html"><span class="kw1228">std::<span class="me2">basic_string</span></span></a><span class="sy1">&lt;</span>CharT<span class="sy1">&gt;</span> s<span class="sy4">;</span>
    <span class="br0">}</span><span class="sy4">;</span>
 
    <span class="kw1">template</span><span class="sy1">&lt;</span><span class="kw1">class</span> CharT<span class="sy1">&gt;</span>
    NestedS<span class="br0">(</span><a href="../string/basic_string.html"><span class="kw1228">std::<span class="me2">basic_string</span></span></a><span class="sy1">&lt;</span>CharT<span class="sy1">&gt;</span><span class="br0">)</span> <span class="sy2">-</span><span class="sy1">&gt;</span> NestedS<span class="sy1">&lt;</span>CharT<span class="sy1">&gt;</span><span class="sy4">;</span>
<span class="br0">}</span><span class="sy4">;</span></pre></div></div></div>
</td>
<td><span class="t-mark-rev t-since-cxx17">(C++17 起)</span></td></tr>
</table>
<h3><span class="mw-headline" id=".E5.B1.80.E9.83.A8.E7.B1.BB">局部类</span></h3>
<p>类声明可出现于函数体内，该情况下它定义<i>局部类</i>。这种类的名字只存在于函数作用域中，且无法在函数外访问。
</p>
<ul><li> 局部类不能拥有静态数据成员
</li><li> 局部类的成员函数无连接
</li><li> 局部类的成员函数必须完全在类体内定义
</li><li> <span class="t-rev-inl t-since-cxx14"><span>除<a href="lambda.html" title="cpp/language/lambda">闭包类型</a>以外的</span> <span><span class="t-mark-rev t-since-cxx14">(C++14 起)</span></span></span>局部类不能拥有成员模板
</li><li> 局部类不能拥有<a href="friend.html#.E6.A8.A1.E6.9D.BF.E5.8F.8B.E5.85.83" title="cpp/language/friend">友元模板</a>
</li><li> 局部类不能在类定义内定义<a href="friend.html" title="cpp/language/friend">友元函数</a>
</li><li> 函数（包括成员函数）内的局部类可以访问其外围函数能访问的相同名字。
</li></ul>
 <table class="t-rev-begin">
<tr class="t-rev t-until-cxx11"><td>
<ul><li> 局部类不能用作模板实参
</li></ul>
</td>
<td><span class="t-mark-rev t-until-cxx11">(C++11 前)</span></td></tr>
</table>
<div class="t-example"><div class="t-example-live-link"><div class="coliru-btn coliru-btn-run-init">运行此代码</div></div>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="cpp source-cpp"><pre class="de1"><span class="co2">#include &lt;vector&gt;</span>
<span class="co2">#include &lt;algorithm&gt;</span>
<span class="co2">#include &lt;iostream&gt;</span>
 
<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span>
<span class="br0">{</span>
    <a href="../container/vector.html"><span class="kw1269">std::<span class="me2">vector</span></span></a><span class="sy1">&lt;</span><span class="kw4">int</span><span class="sy1">&gt;</span> v<span class="br0">{</span><span class="nu0">1</span>,<span class="nu0">2</span>,<span class="nu0">3</span><span class="br0">}</span><span class="sy4">;</span>
    <span class="kw1">struct</span> Local <span class="br0">{</span>
       <span class="kw4">bool</span> operator<span class="br0">(</span><span class="br0">)</span><span class="br0">(</span><span class="kw4">int</span> n, <span class="kw4">int</span> m<span class="br0">)</span> <span class="br0">{</span>
           <span class="kw1">return</span> n <span class="sy1">&gt;</span> m<span class="sy4">;</span>
       <span class="br0">}</span>
    <span class="br0">}</span><span class="sy4">;</span>
    <a href="../algorithm/sort.html"><span class="kw1618">std::<span class="me2">sort</span></span></a><span class="br0">(</span>v.<span class="me1">begin</span><span class="br0">(</span><span class="br0">)</span>, v.<span class="me1">end</span><span class="br0">(</span><span class="br0">)</span>, Local<span class="br0">(</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// C++11 起</span>
    <span class="kw1">for</span><span class="br0">(</span><span class="kw4">int</span> n<span class="sy4">:</span> v<span class="br0">)</span> <a href="../io/cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1">&lt;&lt;</span> n <span class="sy1">&lt;&lt;</span> <span class="st0">' '</span><span class="sy4">;</span>
<span class="br0">}</span></pre></div></div>
<p>输出：
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="text source-text"><pre class="de1">3 2 1</pre></div></div> 
</div>
<h3><span class="mw-headline" id=".E5.8F.82.E9.98.85">参阅</span></h3>
<table class="t-dsc-begin">

</table>

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